I can't just send him back to his mom

I have my 14 year old step son right now. He was living with me and my soon to he ex husband because he was being severely abused by his mother. My husband who is a cop would beat me day in and day out. Honestly I'm starting to think him and his ex wife divorced because they could both beat the shit out if each other and wanted a smaller competition... He pretty much ignored his son and forgot to even give him food so I made sure he ate. One of the worst beatings I ever got my step son tased his father with his on taser and had called the police. From what I've heard my husband is receiving a paid suspension while they decide what to do. They let my step son come with me to my brothers house but my mom lives with my brother and she's had a problem with my step son being here and said I need to cut all ties with my ex... His son included. If I don't take him he could end up in foster care or even back with his mother because of our shitty system. My brother wants to respect my mom so my only option is to go to our savings account. We have 4,000 in there and I'll take my fair half and keep us in a hotel until I figure out a game plan. He saved me.. I can't leave him behind...